The little white poodle was curled up under the wheel of a minivan parked next to San Francisco's Sigmund Stern Grove. The street was wet from recent rains, and her leash trailed out from beneath the car.

I'd just come out of the park, where I'd seen a dog walker unload six or seven dogs from that vehicle and bring them into the off-leash dog play area, leashes trailing just like hers. It was clear she was one of his charges, and he hadn't noticed or didn't care that she'd stayed behind.

One of my dogs is elderly and needed to rest, and my house was just a few yards away. So I brought her home and then returned to the dog park, intending to tell the careless dog walker just what I thought about his powers of observation, and to make sure the little poodle was safe.

Unfortunately, they were both gone when I got there, which meant not only that I didn't get to find out his business name -- or yell at him -- but also that it had been a mighty short walk for his clients' dogs. I doubt he'd been there even 15 minutes.

Anyone who's spent time in one of San Francisco's many parks has seen or heard a story like this one, or worse. There are way too many professional dog walkers who regularly bring more dogs to the park than they can handle, ignore piles of poop, and have no control over their dogs.

So, if you're a dog owner looking for a pro to help keep your dog exercised and out of trouble while you're at work or on vacation, how do you find one of the good ones, and avoid the bad?

I'm lucky enough to have found Courtney Gunter of San Francisco's The Whole Pet. She was voted "Best Pet Sitter in the Bay Area" in Bay Woof Magazine's "Beast of the Bay" competition, and runner up as best dog trainer and best dog walker, too.

Because I prefer to walk my dogs myself, I initially hired Gunter as a pet sitter when I was out of town. But I was so impressed by the care she gave my dogs last year when my mother was dying of cancer, that I asked her to help give my rambunctious, all-play-all-the-time Scottish Deerhound puppy, Rawley, enough exercise when he joined my family in March.

I figured Gunter might have some insider's tips for dog owners in need of a dog walker, and she did. Below are her suggestions for telling the good from the bad in the world of professional dog walkers.

First, narrow the field. "If you live in San Francisco, go to the Animal Care and Control website," she says. "They have really great guidelines for dog walkers and a list of those who abide by them."

Even if you don't live in San Francisco, Gunter adds, the guidelines will give you an idea of what you're looking for in a dog walker. She recommends asking friends, your dog's trainer or your veterinarian for their references. Hang out in dog parks and look for dog walkers who are doing a good job.

Most dog walkers have websites, too, so you can read about their approach and the neighborhoods they serve.

Next, interview the candidates rigorously. "Start by asking how many dogs they walk at a time," Gunter says. "The City of San Francisco guidelines say that each person should walk no more than six dogs. Anyone who doesn't know that, or gives you a higher number, should be avoided."

Good dog walkers will have references and a contract for you to sign. They'll also have clear policies on cancellations for weather, illness or other emergencies. And they tend to get as much information as possible about your dog before signing you up as a client. In fact, they probably will have as many questions for you as you have for them.

"Knowing how to integrate different dogs into a group takes skill and experience," Gunter says. "They need to really get to know the dogs they walk together, so that everyone has a safe and enjoyable experience. If the dog walker doesn't seem to have a handle on that, I'd consider that a pretty big red flag."

Other questions to ask include how they handle first aid, how they deal with behavior problems, and how long they'll keep the dog at the park.

"Just because the dog is out for six hours doesn't mean they're at the park for six hours," Gunter says. "Is your dog just riding around in a van while they pick up 15 other dogs? That's not what you're paying for."

Find out where the dogs go on their walks, too. There are lots of great off-leash areas in San Francisco, and there's no reason to take the dog to the same one every day.

Inquire about the dog walker's business practices. If the business owner has employees, ask how they're screened and trained. Every person who is going to be handling your dog should be investigated as thoroughly as the owner of the company.

You should also find out how your pet will be transported.

"A lot of people don't think to ask about the vehicles that are used, how the dogs are restrained or confined, and how clean the vehicle is," Gunter cautions. Will your dog be traveling in a vehicle that's safe, well-ventilated and kept in good repair?

Go out with the prospective dog walker on a "walk-along." Things to watch for include the dog walker's ability to keep relaxed control of the dogs, not to lose track of any of them, and to notice and clean up after every poop.

Gunter added one more tip: Do they handle themselves in a professional manner? "If they show up in flip-flops yakking on a cell phone, walk away," she says.

Once you've hired a dog walker, the process isn't over. The point of using a professional dog walker isn't just to let your dog have a potty break or even to get exercise, but to keep her mentally and physically healthy -- none of which happens if she spends her time lying under the dog walker's car.

Pay attention to your dog. Is she excited to see the dog walker, or reluctant to go with him? Does she seem tired but happy after her walks, or either over-stimulated or subdued?

There is a bigger picture here, too. As dog owners always say, "A tired dog is a good dog." And good dogs make life better for everyone, including people who don't have dogs at all.

Dogs who are taken out and allowed to run and play until they're ready to drop are far less likely to drive the neighbors crazy with incessant barking. They are less destructive, which should make landlords happy.

And dogs who are regularly socialized with other dogs and people at dog parks will be less likely to create a nuisance when they encounter dogs and people in other places, like a public sidewalk.

Bad dog walkers make their whole profession look bad, and they make life in the city worse for all of us. Make sure you're not giving your money to one of them, for your dog's sake, and everyone else's, too.